Traditional AB output stages typically do not allow the output voltage to substantially go to zero volts. More specifically, most output stages include a pair of complimentary emitter follower transistors that are biased so that there is some overlap, with an emitter follower of an N-type on the top side and an emitter follower of a P-type on the bottom side. In this arrangement, the output can only go within VBE of the upper voltage rail and down to VBE above the lower voltage rail. Thus, if the lower voltage rail is ground, as is often the case in circuits powered by a single power supply, the output can only go as low as about 0.7V. This, however, is not convenient for a video circuit where it is may be desirable to allow the output to approach ground.